The present invention relates to liquid crystal displays (LCDS) and heater systems for heating LCDs and other devices such as flat lamps.
In the past, LCD heater plates have been incorporated to provide a uniform temperature across the LCD surface. The heater has typically been deposited material such as idium tin oxide (ITO) applied to a glass cover placed adjacent to the liquid crystal layer within the display. Electrical current is then passed through the ITO coating across the display face to generate uniform heating. However the thickness and rigidity of the glass cover prevents the use of these heaters with flexible displays and in other environments.
Many available temperature sensors, for providing feedback to thermal control functions related to controlling the LCD heaters, are opaque and too large to be placed within the stacked layers comprising the display. Consequently, the thermal sensors have been placed about the periphery to provide information about the temperature of the LCD material. This method has limitations for determining the temperature of the central portion of the display and the extent of thermal gradients present. Thermal gradients form across the surface of the display due to non-uniform flow of heat from the liquid crystal material to the adjacent environment and display housing.
Thermal sensors designed to be positioned in front of the display are preferably very small so that they are not readily discernable to the eye. For example, thermal sensors can be formed in the ITO coating itself. However, it has been found that the small feature sizes of some such sensors makes it difficult for the sensors to provide the desired temperature sensing accuracy.
Consequently, there exists a need for improved thermal sensing across flexible displays and other heating environments such as flat lamp heaters.
A flexible or standard (rigid) liquid crystal display (LCD) includes an LCD panel providing a surface. A flexible heating system of the invention includes a substantially transparent flexible sheet substrate disposed adjacent the surface of the LCD panel and a substantially transparent resistive heating element formed on the flexible sheet substrate. One or more serpentine shaped thermal sensors are formed in the resistive heating element. Control circuitry coupled to the serpentine shaped thermal sensors and to the substantially transparent resistive heating element and other heaters controls the heating element and other heaters based resistances of the serpentine shaped thermal sensors.